X-ray tube temperature enhanced field emission cathode



ATHODE Nov. 1, 1966 w. P. DYKE ETAL -RAY TUBE TEMPERATURE ENHANCED FIELDEMISSION C Filed Dec. 19, 1961 2 Sheets-Sheet 1 Fig.

INVENTORS.

WALTER P. DYKE FRANK J. GRUNDHAUSER BUCKHORN, CHEATHAM 8 BLORE ATTORNEYSNov. 1, 1966 w. P. DYKE ETAL X-RAY TUBE TEMPERATURE ENHANCED FIELDEMISSION CATHODE 2 Sheets-Sheet 2 Filed Dec.

Fig. 5

Fig. 6

INVENTORS. WALTER F3 DYKE BY FRANK J. GRUNDHAUSER Fig. 7 BUCKHORN,CHEATHAM a BLORE ATTORNEYS Uited States Patent 3,283,203 X-RAY TUBETEMPERATURE ENHANCED FIELD EMlSSlON CATHODE Walter P. Dyke and Frank J.Grundhauser, MeMinnville,

Greg, assignors to Field Emission Corporation,

McMinnville, Greg, a corporation of Oregon Filed Dec. 19, 1961, Ser. No.160,534 16 Claims. (Cl. 313-56) This invention relates to a temperatureenhanced field emission X-ray tube and more particularly to an X-raytube having a conical anode and employing both thermal emission andfield emission of electrons from a cathode structure.

Tubes in accordance with the present invention are of the general typedisclosed and claimed in applicants copending application Serial No.2,033, filed January 12, 1960 now Patent No. 3,179,832 granted Apr. 20,1965. In common with such previously disclosed tube, electrons areemitted from cathode filament wires by a combination of thermal andfield emission and strike an anode at high velocity. The emissioncurrent may, for example, be the order of 2,000 to 4,000 amperes persquare centimeter of emitting surf ce. Sufficient emitting surface maybe provided in the tubes of the present invention so that emissioncurrents of the order of 1,000 to 2,000 amperes or greater may beobtained. Such currents are produced for very short times, for example,times of the order of .l to .2 microsecond and the spacing of the anodesand cathodes is such that the voltage applied between an anode andcathode may be of the order of 300 to 600 kva. or greater and such thatthe tubes have impedances of the order of 300 ohms. The power applied tothe tubes may be of the order of 300 to 1200 million watts or greater.Electrons traveling at extremely high velocities strike the conicalsurface of the anode so that an intense source of X-rays is provided fora very short period of time.

The anodes of the tubes of the present invention are elongated conicalelements with their smaller ends directed toward a wall of the tube inwhich they are employed. Electron emission is from a plurality ofcathode elements arranged in cage-like structure surrounding the anodeand concentric with its axis. The cathode elements are in the form offilament wires and such wires are spaced from each other eithercircumferenti ally of the anode or axially of such anode. The cathodewires are heated to a thermal electron emission temperature by a cathodeheating current and upon supplying a high voltage, high current pulse ofelectric energy to the anode and cathode, electrons are emitted from thecathode elements and travel at high velocity in converging paths towardthe anode. Such electrons repel each other circumferentially of theanode during their travel and the result is a diffused cloud of rapidlytraveling electrons which strike the conical surface of the anode withsubstantially uniform distribution over such surface. The major portionof the conical surface of the anode is thus substantially uniformlybombarded by the electrons so that hot spots and uneven displacements ofmetal from the surface of the anode are avoided. X-rays are emittedsubstantially uniformly from the conical su'rfiace of the anode andsince such anode can be of small diameter, a very intense source ofX-rays of very small area as viewed from the smaller end of the conicalsurfiace of the anode is produced.

"ice

The cathode structure also includes cathode connectors,

one of which connects one end of each of the filament wires together andanother of which connects the other end of each of the filament wirestogether. Such connectors preferably also form the supports for thefilament wires. The surfaces of such connectors which are in thevicinity of the anode and which are directed toward such anode arecarefully smoothed to avoid points or edges of small radius of curvatureto thus avoid undesired electron emission from such connectors.Consistent repeated operation of such tubes requires that such surfacesremain in a smooth condition even though metal particles may be removedfrom the surface of the anode during operation of the tubes anddeposited upon such connectors. The tubes of the present invention aretherefore constructed so that such connectors for the cathode elementsare self-cleaning and self-smoothing. Thus, the connectors forming thesupports for the filament wires are so proportioned in cross sectionrelative to the filament wires that a cathode heating current flowingthrough both such connectors and the filament wires. and of a valuewhich will raise the temperature of the filament Wires to a thermalelectron emission will also raise the temperature of such connectors toa self-cleaning and smoothing temperature. The increase in temperatureof the connectors is partly by conduction of heat from the filamentwires and partly by resistance heating due to the current flow in theconnectors themselves. Such self-cleaning temperatures are of the orderof 1900 to 2000 K. and are below temperatures at which substantialthermal emission of electrons occurs. 4 The cathode structure of thepresent invention lends itself to providing electron emitting areaswhich are substantially greater in total area than the tube of thecopending application referred to above. This means that for a giventotal quantity of electron emission from the cathode elements, theemission per unit area may be reduced, for example, by lowering thetemperature to which the cathode elements are heated. Thus with thetubes of the present invention electron thermal emission temperatures ofthe order of 2700 K. for tungsten filament wires are entirely possibleinstead of the 2900 to 3000 K. contemplated in the copending applicationreferred to above. This results in less deterioration of the cathodestructure and longer tube life.

Also in the construction of the tubes of the present invention, theconnectors or supports for the cathode filament wires may be kept wellaway from the anodes or connections to the anodes such that thelikelihood of unwanted electron emission from points or projectionswhich may occur on such connectors is reduced. The pulses of electricenergy applied to the anode and the cathode are also preferablysufiiciently short that the high voltage of such pulses is removedbefore ions from the anode have reached the cathode wires or cathodeconnectors. The result is that very little material is carried from theanode to the cathode structure and, if the surfaces of the connectors orsupports for the cathode filament wires are initially made very smooth,the heating action referred to retains such smoothness.

The cathode structure described above is preferably surrounded by ashield and focusing element of metal which is ordinarily maintained atsubstantially the same potential as the cathode filament wires but whichmay be maintained at a negative potential relative to the filamentwires. Such element is preferably in the form of a continuous metalliccylinder concentric with the axis of the anode and concentric with thecage formed by the cathode filament wires. By maintaining such shield atsubstantially the same voltage as the cathode during operation of thetube or at a potential somewhat negative with respect to the cathode,the shield acts to focus the electrons emitted from the cathode elementsupon the surface of the anodes by driving such electrons toward thesurface of the anode. Such shield also prevents electron bombardment ofany glass portion of the envelope of the tube by electrons from thecathode as well as preventing any positive ion bombardment due to ionswhich might escape from the anodes and pass between the cathode filamentwires.

The conical anode and the cathode structure just described enables thesmaller end of the anode to be positioned very close to a wall of theenvelope of the tube so that high intensity X-rays can be projected fromsuch tube. That is to say, the X-rays have their highest intensityimmediately adjacent the surface of the anode which is being struck bythe rapidly traveling electrons and for purposes requiring extremelyhigh intensity X-rays, the material being subjected to X-ray radiationmay be placed immediately adjacent the wall of the tube opposite thesmall end of the anode. It is even possible to make the shield of thecathode structure a part of the wall of the envelope of the tube toprovide such shield with an end closure so that the resulting shieldstructure projects from the remainder of the tube. The anode and cathodestructure may then be placed within such shield structure so that theX-ray emitting portion of the tube may be inserted into an aperture in abody to be X-rayed, or treated with X-ray radiation.

It is therefore an object of the present invention to provide an X-raytube in which electrons emitted both by thermal emission and fieldemission are caused to strike the conical surface of a conical anode.

Another object of the invention is to provide an X-ray tube in which acathode structure made up of a plurality of spaced filament wiressurrounds the conical surface of a conical anode in order to produce adiffused cloud of rapidly traveling electrons striking such surface whena high voltage, high current pulse of electric energy is supplied tosuch cathode and anode.

Another object of the invention is to provide an X-ray tube in which acathode structure made up of a cage of heated filament wires is employedto emit electrons both by thermal emission and field emission and inwhich a shield and focusing structure causes such electrons to strikethe conical surface of an anode positioned within such cage in a mannerin which the electrons striking the anode are substantially uniformlydistributed over the surface of such anode.

A further object of the invention is to provide an X-ray tube capable ofproducing intense pulses of X-ray radiation in which the anode surfacefrom which such radiation emanates is positioned closely adjacent thewall of such tube so that intense radiation is present immediatelyexternally of such wall.

A still further object of the invention is to provide an X-ray tubecapable of producing intense pulses of X-rays and in which such Xraysmay be produced in a small portion of the envelope projecting from themain portion envelope of such tube.

A still further object of the invention is to provide an X-ray tube inwhich a cage-like cathode structure made up of filament wires extendingbetween connectors forming supports for such wires surrounds the conicalsurface of a conical anode and in which heating the connectors of suchcage structure to a surface cleaning and smoothing temperature occurswhenever the filament wires are heated to a suitable thermal electronemission temperature.

Other objects and advantages of the invention will appear in thefollowing description of preferred embodiments shown in the attacheddrawing of which:

FIG. 1 is a view of an X-ray tube in accordance with the presentinvention partly in side elevation and partly in axial section;

FIG. 2 is a partial axial sectional view of one end of the tube of FIG.1 on an enlarged scale and taken on the line 2--2 of FIG. 1;

FIG. 3 is a transverse vertical section of the tube of FIGS. 1 and 2,taken on the line 3-3 of FIG. 2;

FIG. 4 is an end elevation on the same scale as FIGS. 2 and 3 of thetube of FIGS. 1 to 3, looking to the right in FIG. 1;

FIG. 5 is a view similar to FIG. 2 of a modified tube structure;

FIG. 6 is a side elevation of a modified X-ray tube in accordance withthe present invention with parts broken away to show internal structure;

FIG. 7 is an end elevation of the tube of FIG. 6 looking to the right insuch figure with parts broken away to show internal structure;

FIG. 8 is a side elevation of a modified cathode structure, usable inany of the tubes of the present invention;

FIG. 9 is a transverse vertical section through the cathode structure ofFIG. 8, taken on the line 9--9 of FIG. 8;

FIG. 10 is a view similar to FIG. 8, showing a further modified cathodestructure and also a conical anode in position in such structure; and

FIG. 11 is a transverse section of the cathode structure of FIG. 10, astaken on line 11-11 of FIG. 10.

The X-ray tube shown in FIGS. 1 to 4 of the drawing includes anelongated cylyindrical envelope 20 having a reentrant portion 22 at oneend thereof. Such reentrant portion terminates at its inner end in a cap24 of suitable metal having a thermal cocfiicient of expansion similarto that of glass of the reentrant portion 22. An anode support member 26in the form of an elongated rod extends through the cap 24 in sealingrelation therewith and terminates at its end within the reentrantportion 22 in a socket member 28 for the reception of a conductor suchas the inner conductor of a coaxial cable. As shown in FIG. 2, the otherend of the anode support member 26 terminates in a conical anode element30 having its axis extending substantially concentric with the axis ofthe envelope 20.

The anode element 30 is surrounded by a cathode structure 32 including apair of axially spaced cathode connectors 34 and 36, each formed of arelatively heavy wire bent into an annular portion. Lead portions 38projector radially from the annular portion of the connector 34. Suchlead portions extend parallel to each other and, as shown most clearlyin FIG. 1 and FIG. 2, are secured at their ends to a cathode connectorpin 42 extending to the exterior of the tube and mounted in andinsulated from a metal cap 44 forming an end closure for the envelope 20at the end opposite the reentrant portion 22. Similar lead portions 40project radially from the annular portion of the connector 36 and extendparallel to each other. The lead portions 40 are secured to a connectorpin 46 mounted in and also insulated from the cap 44 so as to extendaxially of the tube to the exterior thereof. The lead portions 38 and 40thus form supports as well as electrical connections for the cathodestructure 32.

A plurality of filament wires 48 are welded to the annular portions ofthe connectors 34 and 36 and extend in a direction axially of the anode30 between such portrons. Each of the filament wires 48 thus has one endconnected to a connector 34 and its other end to a connector 36. Suchwires are uniformly spaced circumferentially around the anode 30 andform a cathode cage surrounding and concentric with the axis of theanode element 30. The filament wires will ordinarily each be of theorder of 5 to 20 mils in diameter, while the wires of the annularportions of the connectors will, in general, be of a diameter providinga cross-sectional area somewhat larger than the total of cross-sectionalarea of the filament wires. It will be apparent from the drawing thatthe filament wires 48 are straight wires extending between theconnectors 34 and 36, i.e., they are uncoiled filament wires.

A hollow cylindrical shield and focusing member 50 surrounds the cageformed by the filament wires 48 of the cathode structure 32. Suchcylindrical shield 50 may be supported by a plurality of support rods 52secured to the end cap 44 of the tube at one of th ir ends and to theshield 50 at the other of their ends, for example, by spot welding.

A getter element 54 is also shown in FIG. 2 as being positioned within ashielding member 56 and as having one end connected to the connector pin58 extending through and insulated from the cap 44. It will beunderstood that the other end of the getter element 54 will be connectedto one of the filament leads, such as the lead 38, so that such gettermay be heated during evacuation of the tube.

The cap 44 has an aperture 60 therein which is aligned with the end ofthe anode element 30. A thin element 62 of a suitable metal is securedto the cap 44 so as to cover such aperture and form a substantiallytransparent window for X-rays generated on the conical surface of theanode element 30.

In operation of the tube of FIGS. 1 to 4, a suitable source of filamentcurrent is connected between the connector pins 42 and 46 so as tosupply heating current to the cathode structure 32. With tungstenfilament wires, the heating current is sufficient to raise thetemperature of the filament wires 48 of the cathode structure 32 to atemperature of approximately 2700 K. and is applied to the cathodestructure a short time before a high voltage, high current pulse ofelectric energy is applied to the anode and cathode of the tube. Theconnectors 34 and 36 are so proportioned in size with respect to thefilament wires that for tungsten connectors, the temperature thereof israised to approximately 1900-2000 K. during heating of the cathode. Thecap 44 of the tube is either connected to one of the cathode connectorpins 42 or 46, or is connected to a voltage somewhat negative to that ofeither of pins 42 or 46. A high voltage, high current pulse of electricenergy is then impressed between the anode 30 and the cathode structure32 by suitable connections to the socket 28 of the anode support 26 andto one side of the filament heater circuit through one of the connectorpins 42 and 46. Such pulse may be from a pulser of the type disclosed inthe copending application of Dyke, Grundhauser and Stunkard, Serial No.103,796, filed April 18, 1961, and may be the order of 300 to 600 kv. orgreater with the current of 10004000 amperes or greater and for a timeranging from .1 to .2 microsecond.

Electrons are emitted from the filament wires by both field emission andthermal emission and such electrons travel at extremely high velocitytoward the anode and strike the conical surface of the anode. Suchelectrons form a diffused cloud of electrons traveling at high velocityso that substantially all portions of the conical surface of the anodeare struck by such electrons. A high intensity pulse of X-rays isproduced and viewing the anode from its smaller end, such electrons areproduced from a very small projected area. This provides high resolutionof X-ray photographs.

The extremely short pulses of electrical energy at high voltage, whichare employed to energize the tube of the present invention, causeelectrons to travel at speed approaching the speed of light toward theanode and such electrons strike the anode before such pulse ceases.However, there is not sufiicien-t time for any positive ions which maybe produced at the anode to reach the cathode before the pulse ceases.Thus very little material removed from the surface of the anode byelectron bombardment travels as far as the cathode structure and most ofany of such material passes between the cathode filament wires and isstopped by the shield 50. Such shield therefor not only has a focusingeffect causing the electrons to be directed toward the anode but alsoprotects the envelope of the tube against ions or any other particlestraveling radially outward from the anode. The heating of the connectors34 and 36 to a heating and smoothing temperature substantiallyeliminates any deposition of such particles upon the surfaces of theconnectors and substantially eliminates unwanted electron emission fromsuch surfaces to thus eliminate the production of X-rays from other thanthe conical surface of the anode. The heating current is preferablydiscontinued immediately after a pulse of X-ray radiation has thus beenproduced and is again supplied just prior to the production of anotherpulse of such radiation.

The tube of FIG. 5 is similar to the tube of FIGS. 1 to 4 but has amodified cathode structure 63 and end cap 64. Such cap has an axiallyprojecting portion 68 in which the cathode structure 63 is positionedand which forms a shield for the cathode structure. Such projectingshield 68 has a cathode connector .76 in the form of an annular ring ofwire positioned within its end which is remote from the remainder of thecap 64. Such ring is supported 'in spaced relation to the shield 68 byspaced support portions 72. A similar connector 74 is positioned Withinthe shield 63 at its end adjacent the remainder of the cap 64 and issimilar in form to the connectors 34 and 36 of the tube of FIGS. 1 to 4.Such connector 74 has lead and support portions 76 secured to a cathodeconnector pin 78 extending to the exterior of the tube and supported inand insulated from the cap 64.

The two connectors 76 and 74 have axially spaced annular portionsconcentric with the shield 68 and with the anode element 30. A pluralityof filament wires 86 are secured at their ends to such annular portionsand extend axially of the tube to form a cathode cage around the conicalanode element 30. Such anode element may be of the same construction asthe anode element 30 of the tube of FIGS. 1 to 4. The cap 64 may haveanother cathode connector pin 82 secured to and connected to such cap so.that heating current can flow from such pin through the cap 64 and thenthrough the support portions 72, connector 76, filament wires 80, andconnector 74 including support portions 76 to the pin 78. A metallicwindow 62 is secured to and closes an aperture in the projecting end ofthe shield 68.

The operation of the tube of FIG. 5 may be entirely similar to thatdescribed with respect to the tube of FIGS. 1 to 4. The major dilierencein tube construction is that the anode 30 is positioned closer to theend wall of the tube having the metallic window 62 substantiallytransparent to X-rays so that the high intensity of X-rays immediatelyadjacent the anode can be brought nearer to the object or material beingX-rayed or being subjected to X-ray radiation. It will be apparent thatthe cap 64 may be at ground potential and that the projecting portions63 of the cap 64 may be inserted into an aperture in an article beingX-rayed.

The tube of FIGS. 6 and 7 is similar to the tubes of FIGS. 1 to 5, butthe anode 3t) and a modified cathode structure 82 are shown as beingpositioned in a glass envelope having a right angle bend therein so thatthe connector pins 84 and S6 for the cathode heater circuit can bemounted in a metal cap 88 which is out of the path of the usable X-raysproduced by the tube. The cathode structure 32 of the tube of FIGS. 6and 7 may be very similar to the cathode structure 32 of the tube ofFIGS. 1 to 4 and may be supported by connectors 91 and 92 secured to andconnected to the connector pins 84 and 86, respectively. The shield 94may be similar to the shield 5d of FIGS. 1 to 4 and may surround thecathode structure 82 and be supported upon support elements 96 securedto and extending from the cap 88. A getter element 100 may have oneterminal connected to a connector pin 98 and its other end connected toone of the connector pins 84 or 86.

In the tube of FIGS. 6 and 7, the usable X-rays are projected throughthe left end of the tube as viewed in FIG. 6 and the anode can bepositioned quite close to the wall of the envelope of the tube. Theoperation of the tube of FIGS. 6 and 7 may be entirely similar to thatdescribed with respect to the tubes of FIGS. 1 to 4 and the tube of FIG.5.

A modified cathode structure 102 of a type usable with any of the tubesdescribed above instead of the cathode structures 32, 63 or 82, is shownin FIGS. 8 and 9. Such cathode structure 102 includes a cylindrical gridstructure made up of a plurality of conducting portions 104 extendingaxially of the cylindrical structure and joined together by a pluralityof oircumferentially extending conductor portions 106 which formintermediate supports for the conducting portions 104. The ends of thegrid structure thus formed are secured to axially spaced con nectors 1G8and 110 which may be similar in form to the connectors 34 and 36 of thetube of FIGS. 1 to 4. Such connectors may have support portions 112 and114 projecting radially therefrom so that the cathode structure 102 maybe suitably supported in a tube, for example, in the same manner as thecathode structures 32 of FIGS. 1 to 4. It will be apparent that theconductor portions 104 are, in fact, filament wires extending betweenthe connectors 110 and 112 and that the operation of tubes containingthe cathode structures of FIGS. 8 and 9 is substantially similar to thatof the other tubes described above.

The cathode structure of FIGS. 10 and 11 is similar to that of FIGS. 8and 9, except that the conductor portions 124 which form the filamentwires extend circumferentially of the cathode structure instead ofaxially thereof. Such conductor portions have their ends connected toconnectors 126 and 128 extending longitudinally of the cathodestructure. The various conductor portions 124 may have intermediateportions connected together by connector portions 128 so that thecathode structure is in the form of a hollow cylindrical gridsurrounding the anode 30. The connectors 125 and 123 may have lead andsupport portions 131) and 132 for supporting the cathode structure in atube and for forming heating current connections for the cathodestructure. It will be understood that a shield similar to the shield 50of the tube of FIGS. 1 to 4 will be positioned around the cathodestructures of FIGS. 8 to 11 and that with slight modification, suchcathode structures may be employed in tubes of the type shown in FIG. 5or in FIGS. 6 and 7. The cathode structures of FIGS. 8 and 9 may bemade, for example, by photoetching apertures in a tubular metal memberhaving thin walls or in the case of FIGS. 10 and 11, by etchingapertures in a thin sheet of metal which is later formed into a slottedtubular member.

The anode elements and also the filament wires and cathode connectorsand supports of the various cathode structures described above arepreferably made of tungsten although other refractory metals may beemployed. The other elements such as the support elements for the anodeand cathode structures are also preferably made of tungsten but may bemade of various other metals. The caps 24, 44, 64 and 88, which aresealed directly to portions of the glass envelopes of the tubes may beof any suitable alloy having a thermal temperature coefiicient ofexpansion similar to that of the glass employed, and a number ofcombinations of glass and such alloys are available commercially. Theconical anode can be quite small in diameter at its large end, forexample, of the order of 50 to 100 mils, and have a small angle betweenthe elements of its conical surface and its axis, for example, of theorder of 7.

While I have disclosed the preferred embodiments of my invention, it isapparent that the invention is not to be limited to details thereof butthat the scope of the invention is to be determined by the followingclaims.

We claim:

1. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means extending to the exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of uncoiled filament wirespositioned around said anode and spaced from each other andsubstantially parallel to each other and radially spaced from saidanode,

and cathode connector means including electrical connections extendingfrom the opposite ends of said filament wires to the exterior of saidenvelope to provide for heating said filament wires and causing theemission of electrons from said filament wires by combined fieldemission and thermal emission.

2. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode positioned in said envelope,

anode connector and support means providing an electrical connectionextending to the exterior of said envelope,

a hollow cylindrical combined field emission and thermal emissioncathode structure in said envelope and concentrically surrounding saidanode,

said cathode structure including a plurality of uncoiled filament wirespositioned around said anode and spaced from each other andsubstantially parallel to each other and radially spaced from saidanode,

cathode connector and support means including electrical connectionsextending from the opposite ends of said filament wires for connectingsaid wires in parallel and extending to the exterior of said envelope toprovide for heating said filament wires and causing the emission ofelectrons from said filament wires by combined field emission andthermal emission,

and an elongated hollow cylindrical shield concentrical- 1y surroundingand radially spaced from said cathode structure.

3. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode positioned in said envelope,

anode connector and support means providing an electrical connectionextending to the exterior of said envelope,

a combined field emission and thermal emission cathode structureincluding an elongated circular cage of uncoiled filament wiressupported in said envelope and concentrically surrounding said anode,

said filament wires being spaced from each other and substantiallyparallel to each other and being radially spaced from said anode,

cathode connector means making electrical contact with the opposite endsof said wires for connecting said wires in parallel and extending to theexterior of said envelope to provide for heating said filament wires andcausing the emission of electrons from said filament wires by combinedfield emission and thermal emission,

an elongated hollow circular shield of electrical conducting materialconcentrically surrounding and radially spaced from said cage,

and means for supporting said shield in said envelope and providing anelectrical connection thereto to the exterior of said envelope.

4. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

said anode and substantially parallel to each other and spaced from saidanode and from each other axially of said anode,

a cathode connector means connecting one end of each of said wirestogether,

a similar cathode connector means connecting the other end of each ofsaid Wires together,

said cathode connectors including electrical connections extending tothe exterior of said envelope to provide for heating said filament wiresand causing the emission of electrons from said filament wires bycombined field emission and thermal emission,

an elongated hollow circular shield of conducting materialconcentrically surrounding and radially spaced from said cathodestructure,

and means for supporting said shield in said envelope and providing anelectrical connection to said shield from the exterior of said envelope.

11. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a cathode structure supported in said envelope and surrounding saidanode,

said cathode structure including a plurality of filament Wires spacedfrom each other and substantially parallel to each other and radiallyspaced from said anode,

a cathode connector means connecting one end of each of said wirestogether, a similar cathode connector means connecting the other end ofeach of said wires together,

said cathode connectors providing cathode electrical connectionsextending from said connectors to the exterior of said envelope, andhaving portions adjacent said anode which are greater in cross-sectionalarea than the combined cross-sectional areas of said filament wires andproportioned with respect to said filament Wires to provide for heatingsaid portions to a surface cleaning and smoothing temperature below athermal electron emission temperature when a filament heating current ispassed in series through said cathode connector means and said wires inan amount heating said wires to a thermal electron emission temperature.

12. An X-ray tube comprising:

an evacuated envelope an elongated conical anode supported in saidenvelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

an elongated circular cage of filament wires supported in said envelopeand concentrically surrounding said anode,

said filament wires being spaced from each other and substantiallyparallel to each other and being radially spaced from said anode,

cathode connector means making electrical contact with the opposite endsof said wires and providing electrical connections connecting said wiresin parallel and extending to the exterior of said envelope,

and an elongated circular shield concentrically surrounding and radiallyspaced from said cage,

said cathode connector means having their portions adjacent said anodegreater in cross-sectional area than the combined cross-sectional areasof said filament wires and proportioned with respect to said filamentwires to provide for heating said portions to a surface cleaning andsmoothing temperature be low a thermal electron emission temperaturewhen a filament heating current is passed in series through said cathodeconnector means and said wires in an amount heating said wires to athermal electron emission temperature.

13. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of uncoiled filament wirespositioned around said anode and spaced from each other andsubstantially parallel to each other and radially spaced from saidanode,

cathode connectors including electrical connections extending from theopposite ends of said filament wires to the exterior of said envelope toprovide for heating said filament wires and causing the emission ofelectrons from said filament wires by combined field emission andthermal emission,

said anode having its smaller end adjacent and directed toward a wall ofsaid envelope.

14. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connec tion extending tothe exterior of said envelope,

an elongated circular cage of uncoiled filament wires supported in saidenvelope and concentrically surrounding said anode,

said filament wires being spaced from each other and substantiallyparallel to each other and being radially spaced from said anode,

cathode connector means making electrical contact with the opposite endsof said wires and including cathode electrical connections extending tothe exterior of said envelope to provide for heating said filament wiresand causing the emission of electrons from said filament wires bycombined field emission and thermal emission,

and an elongated hollow circular shield concentrically surrounding andradially spaced from said cage,

said anode having its smaller end adjacent and directed toward a wall ofsaid envelope.

15. An X-ray tube comprising:

an evacuated envelope,

a conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

an elongated circular cage of filament wires supported in said envelopeand concentrically surrounding said anode,

said filament wires being spaced from each other and substantiallyparallel to each other and being radially spaced from said anode.

cathode connector means making electrical contact with the opposite endsof said wires and providing cathode electrical connections extending tothe exterior of said envelope,

and an elongated hollow circular shield concentrically surrounding andradially spaced from said cage,

said shield having an end wall and being a part of said envelope andprojecting in a direction axially of said shield from the remainder ofsaid envelope,

said anode having its smaller end adjacent and directed toward said endwall.

16. An X-ray tube comprising:

an evacuated envelope,

a conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

an elongated circular cage of filament wires supported in said envelopeand concentrically surrounding said anode,

said filament wires being spaced from each other and substantiallyparallel to each other and being radially spaced from said anode,

cathode connector means making electrical contact with the opposite endsof said wires and providing cathode electrical connections extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of similar uncoiledfilament wires positioned around said anode and spaced from each otherand substantially parallel to each other and radially spaced from saidanode,

a cathode means connecting one end of each of said wires together, and asimilar cathode connector means connecting the other end of each of saidwires together,

said cathode connector means including cathode electrical connectionsextendiing to the exterior of said envelope to provide for heating saidfilament wires and causing the emission of electrons from said filamentwires by combined field emission and thermal emission.

5. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of similar filament wiresextending axially of said anode and substantially parallel to each otherand radially spaced from said anode and spaced from each othercircumferentially around said anode,

a cathode connector means connecting one end of each of said wirestogether,

and a similar cathode connector means connecting the other end of eachof said wires together,

said cathode connector means including cathode electrical connectionsextending to the exterior of said envelope to provide for heating saidfilament wires and causing the emission of electrons from said filamentwires by combined field emission and thermal emission.

6. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of similar uncoiledfilament Wires extending axially of said anode and substantiallyparallel to each other and radially spaced from said anode and spacedfrom each other circumferentially around said anode,

reinforcing elements extending circumferentially of said cathodestructure and connecting said filament wires together at intermediatepoints along their lengths,

a cathode connector means connecting one end of each of said wirestogether,

and a similar cathode connector means connecting the other end of eachof said wires together,

said cathode connector means including electrical connections extendingto the exterior of said envelope to provide for heating said filamentwires and causing the emission of electrons from said filament wires bycombined field emission and thermal emission.

7. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of similar uncoiledfilament wires extending axially of said anode and substantiallyparallel to each other and radially spaced from said anode and spacedfrom each other circumferentially around said anode,

a cathode connector means connecting one end of each of said wirestogether,

a similar cathode connector means connecting the other end of each ofsaid wires together,

said cathode connector means including electrical connections extendingto the exterior of said envelope to provide for heating said filamentwires and causing the emission of electrons from said filament wires bycombined field emission and thermal emission,

an elongated hollow circular shield of conducting materialconcentrically surrounding and radially spaced from said cathodestructure,

and means for supporting said shield in said envelope and providing anelectrical connection to said shield from the exterior of said envelope.

8. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of similar uncoiledfilament wires extending circumferentially around said anode andsubstantially parallel to each other and spaced from said anode and fromeach other axially of said anode,

a cathode connector means connecting one end of each of said wirestogether,

and a similar cathode connector means connecting the other end of eachof said wires together,

said cathode connector means including electrical connections extendingto the exterior of said envelope to provide for heating said filamentwires and causing the emission of electrons from said filament wires bycombined field emission and thermal emission.

9. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of similar uncoiledfilament wires extending circumferentially around said anode andsubstantially parallel to each other and spaced from said anode and fromeach other axially of said anode,

reinforcing elements extending axially of said cathode structure andconnecting said filament wires together at intermediate points alongtheir lengths,

a cathode connector means connecting one end of each of said wirestogether,

and a similar cathode connector means connecting the other end of eachof said wires together,

said cathode connector means including electrical connections extendingto the exterior of said envelope to provide for heating said filamentwires and causing the emission of electrons from said filament wires bycombined field emission and thermal emission.

10. An X-ray tube comprising:

an evacuated envelope,

an elongated conical anode supported in said envelope,

anode connector means providing an electrical connection extending tothe exterior of said envelope,

a combined field emission and thermal emission cathode structuresupported in said envelope and surrounding said anode,

said cathode structure including a plurality of uncoiled filament wiresextending circumferentially around l3 l4 and an elongated hollowcircular shield means concen- References Cited by the Examiner iraigzllysurrounding and radially spaced from said UNITED STATES PATENTS saidshield means having an end wall and being a part 2,097,002 10/1937Thauer 313-56 of said envelope and projecting in a direction axially 521132320 9/1938 3 of said shield from the remainder of said envelope,3333 1 g p 3' said shield means forming a part of said cathode conulpersat a nector means and providing part of the electrical con- HERMAN KARLSAALBACH Primary Examiner nection to one end of said Wires,

said anode having its smaller end adjacent and directed 10 GEORGEWESTBY: Examine"- toward said end Wall. S. CHATMON, 111., AssistantExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,283,203 November 1, 1966 Walter P. Dyke et a1 It is hereby certifiedthat error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below.

Column 4, line 51, for "projector" read project column 9, line 27,before "filament" insert uncoiled Signed and sealed this 5th day ofSeptember 1967.

( A Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. AN X-RAY TUBE COMPRISING: AN EVACUATED ENVELOPE, AN ELONGAED CONICALANODE SUPPORTED IN SAID ENVELOPE, ANODE CONNECTOR MEANS EXTENDING TO THEEXTERIOR OF SAID ENVELOPE, A COMBINED FIELD EMISSION AND THERMALEMISSION CATHODE STRUCTURE SUPPORTED IN SAID ENVELOPE AND SURROUNDINGSAID ANODE, SAID CATHODE STRUCTURE INCLUDING A PLURALITY OF UNCOILEDFILAMENT WIRES POSITIONED AROUND SAID ANODE AND